Arachni is smart, it trains itself by learning from the HTTP responses it receives during the audit process. Unlike other scanners, Arachni takes into account the dynamic nature of web applications and can detect changes caused while traveling through the paths of a web application’s cyclomatic complexity. This way attack/input vectors that would otherwise be undetectable by non-humans are seamlessly handled by Arachni.

Finally, Arachni yields great performance due to its asynchronous HTTP model (courtesy of Typhoeus). Thus, you’ll only be limited by the responsiveness of the server under audit and your available bandwidth.

Note: Despite the fact that Arachni is mostly targeted towards web application security, it can easily be used for general purpose scraping, data-mining, etc with the addition of custom modules.

Module, report and plugin writers are allowed to easily and quickly create and deploy their components with the minimum amount of restrictions imposed upon them, while provided with the necessary infrastructure to accomplish their goals. Furthermore, they are encouraged to take full advantage of the Ruby language under a unified framework that will increase their productivity without stifling them or complicating their tasks.

Although some parts of the Framework are fairly complex you will never have to deal them directly. From a user’s or a component developer’s point of view everything appears simple and straight-forward all the while providing power, performance and flexibility.

There is a new version of Arachni which features numerous optimizations, new modules, new plug-ins and a brand new, although experimental, Web user interface (adding support for distributed deployment, parallel scans and basic report management).

Cheers to the admin for posting it.
However you shouldn’t download the zipball in the description as it is only the source.
Instead, install it using one of the ways described in the following link:http://zapotek.github.com/arachni/#Installation